Glyphosate is the most widely used herbicide in the world. It is a broad spectrum herbicide, meaning it controls both narrow leaf grass and broad leaf weed. Since it has very limited solubility in water, glyphosate acid is usually first converted to a soluble salt. Examples are isopropyl amine (IPA), monoethanol amine (MEA), diethanol amine (DEA), triethanol amine (TEA), sodium (Na), potassium (K), ammonium (NH4), and trimesium.
IPA glyphosate (with some surfactants) was first commercialized as ROUNDUP® Original by Monsanto because it was relatively easy to formulate. Glyphosate formulations with other salts, in particular the ammonium and potassium, have been introduced to market recently.
Use of a concentrated aqueous formulation of glyphosate in the form of a salt made with the inorganic base ammonia and potassium is advantageous Ammonia and potassium are low in costs, readily available, low in molecular weights, and are relatively soluble in water. Additionally, they are natural nutrients for the growth of plants and other organisms.
The use of ammonium and potassium salts of glyphosate for preparing aqueous concentrate formulations of glyphosate suitable for killing and controlling plants has, however, been somewhat limited due to difficulties arising from chemical and physical properties of the ammonium and potassium salts of glyphosate, and lack of biologically suitable surfactants for preparing high-loaded liquid concentrates of such salts. If the biologically suitable surfactants are used, the surfactants tend to lack the property of thickening the glyphosate formulation to desirable viscosity even at highest glyphosate concentration allowable for a liquid formulation. The desired high viscosity in ROUNDUP® Original formulation arises mainly from the IPA as the counterion for glyphosate and not from the surfactant used in the formulation. If K and NH4 glyphosate is formulated into the same 360 g/l, the viscosity is much lower than ROUNDUP® Original. As a matter of fact, even at much higher concentration, such as 540 g/l, the viscosity of the K glyphosate formulation (e.g., ROUNDUP® WeatherMax, 45 cps/22° C.) is still lower than the viscosity of the ROUNDUP® Original (54 cps/22 ° C.). Glyphosate rates and concentrations given herein, even where the glyphosate is present as a salt or salts, are expressed as acid equivalent (ae) unless the context demands otherwise.
Because of the much lower viscosity exhibited in lower than 360 g/l in the case of IPA-glyphosate or in 360 g/l in the case of K- and NH4-glyphosate formulations, many farmers feel that they are being short changed by manufacturers in that they are receiving a watered down product.
Over the years, there has been a request from market place for a glyphosate thickener to improve formulation aesthetics. Accordingly, thick glyphosate formulations, especially the K and NH4 glyphosate formulations, are needed in the market place. However, thickening a glyphosate formulation to desired viscosity, typically 40 cps or higher, is technically challenging. For example, it has previously not been possible to thicken a K and NH4 glyphosate formulation in the concentration range of 360 to 540 g/l. Gelling a glyphosate formulation presents even bigger challenges. When attempting to thicken such formulations, those skilled in the art commonly use water-soluble polymeric thickeners. However, none of the commonly used polymer thickeners works in concentrated glyphosate formulations because they lose their thickening ability as they have a tendency to separate out of solution.
Viscosity requirements vary depending on the specific application. For example, a wiper application requires the formulation to have higher viscosity. Glyphosate formulations generally have higher viscosity as the concentration of glyphosate increases. Farmers sometimes use undiluted Roundup® Original in the wick application to insure high enough viscosity to minimize dripping off. However, use of the undiluted Roundup® Original in the wick application is uneconomical as in those cases it is desirable to use a less concentrated glyphosate. However, use of less concentrated glyphosate formulations presents a potential dripping problem due to low viscosity. Therefore, there is need to thicker diluted glyphosate formulations for wick application to reduce the dripping.
During the spraying application of a dilute pesticide solution, some fine droplets have the potential to drift with wind to unintended area causing damage to the crops in the area. Farmers typically use a water soluble polymer such as guar gum as the drift control agent to control the drift. It is well known that even a small increase in viscosity (˜2-3cps) caused by addition of the guar gum in the dilute pesticide solution has significant effect on drift.
The present inventors have discovered that certain classes of nitrogen containing surfactants can thicken glyphosate formulations very effectively.